Objective: Findings regarding small nerve fiber damage in complex regional pain syndrome type I (CRPS-I) are not uniform, and studies have not included a matched healthy control group. The aim was to assess intraepidermal nerve fiber density (IENFD) in relation to thermal sensitivity of the same skin areas in CRPS-I patients and a gender- and age-matched healthy control group.

Methods: IENFD was investigated in skin biopsies from the CRPS-affected and contralateral limbs of eight CRPS-I patients and from an equivalent site in eight gender- and age-matched healthy controls (HCs). Thermal thresholds (cold/warm detection, cold- and heat-pain detection) were assessed on the affected limb, the matching contralateral limb, and on the equivalent limbs of HCs, and participants rated the intensity of cold/heat and pain to static thermal stimuli (5 °C and 40 °C).

Results: IENFD was significantly lower in both the affected and contralateral limbs of CRPS-I patients than HCs, but IENFD did not differ between the affected and contralateral limbs of patients. The heat pain threshold was lower in the affected CRPS-I limb than in HCs, but all other thermal thresholds were similar in both groups. CRPS-I patients rated the cold stimulus as colder and more painful in the affected limb, and the warm stimulus as hotter, bilaterally, than the HCs.

Conclusions: CRPS-I may be associated with bilateral small fiber damage, and perhaps small fiber neuropathy and bilateral disturbances in thermo-sensory perception. These disturbances could stem from a systemic response to injury or might increase the risk of developing CRPS-I after physical trauma.